🔧 [#1155] -- ensure the X-Session-Expires-In is exposed to CORS requests

The SDK (in embedded formmust be able to read this response header.

src/openforms/conf/base.py

@@ -631,7 +631,7 @@
 CORS_ALLOW_HEADERS = list(default_cors_headers) + config(
     "CORS_EXTRA_ALLOW_HEADERS", split=True, default=[]
 )
-CORS_EXPOSE_HEADERS = []
+CORS_EXPOSE_HEADERS = ["X-Session-Expires-In"]
 CORS_ALLOW_CREDENTIALS = True  # required to send cross domain cookies
 
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